I guess I'm not really understanding completely
why you want the information. In what way has your previous IQ testing interfered with your goals and aspirations?
It sounds as though you'd like a higher number to serve as...
motivation for self-improvement?
a boost to your self-esteem?
explanation for a feeling of alienation from most people you know?
a desire to feel superior to others?
a way to make up for feelings of disappointment regarding your education/career/accomplishments?
a factor in deciding a path forward in your life?
What if 115
is your IQ? Modern research has suggested that IQ may not be as static throughout a lifetime as was previously assumed. Perhaps your actual IQ has drifted downward over time as you've underachieved.
How will that make you feel?
Supposing that your IQ is 150-- what then?
There is a risk in that number becoming a burden in a variety of ways, a (false) badge of honor that defines you, or even an emblem of wasted potential and shame/guilt.
My advice is to ask yourself very carefully
what use this information will be to you, and to examine your reasons for wanting it.It won't make you a different person. It won't change the past. It won't entitle you to much of anything. It
might change your self-perception fairly significantly; that might be a good thing if the results are
better than you expect, and it might be a worse thing if they aren't.
You also asked something that I found quite odd:
"Is it possible to develop a healthy identity without being surrounded by other gifted individuals?"
Forgive me for saying so, but it
sounds as though you are wondering if diversity is "harmful" to the development of a sound self-image, ultimately. I think that is obviously absurd in its own terms.
If by this you meant "affirmation" of gifted traits, then yes, exposure to other gifted people seems to be reassuring to such children, and lead to healthier development (which is an argument in favor of ability grouping and gifted identification in schools).
Most of the people I encounter in the course of living my life are distinctly average and not at all gifted, and this has always been true. Furthermore,
it's entirely irrelevent to them that I am gifted.
(If I
offer my credentials/bona fides out of context, in fact, I have probably just irrevocably labeled myself as socially illiterate or worse.) This may come as a shock, but-- nobody gives me a special express lane at the grocery store, a passing lane all my own on the freeway, or special consideration at book club meetings. Not for my PhD, not for my IQ score. Upsetting, truly-- I
earned that degree through my own hard work, after all.

While I can (sort of) understand wanting an IQ number, knowing the number really doesn't change anything about an adult's life circumstances. In children, there is a very fundamental reason to know; that being that gifted children are almost inherently
asynchronous in development. Presumably this is not really true for most adults over the age of about 26.
My IQ really doesn't define me, and in some ways, being fully aware of possessing a number over 150 makes life
harder, not easier. Why? Because it invites me to limit "intellectual peers" in an inherently artificial (and unhealthy) manner.
Some average people have things to teach me about being a better person, or a happier, more fulfilled one. I have certainly learned patience and compassion from those whose processing speeds are slower than mine. I don't pick potential friends by what their IQ's are-- because it's inherently not a very sensible thing to do. (I say that from the perspective of being 45 years old, however.) When you've seen one gifted person, you've seen ONE, basically, and that is also true for ALL people.
My spouse's IQ value is lower than mine. Significantly so, in fact-- about 10 points on averaging multiple measurements. The reality, however, is that he is far more 'mathy' than I am and probably has a faster processing speed numerically, but my spatial skills and raw problem-solving ability exceed his. On the old S-B, that latter ability led to my higher scores. The day-to-day reality is that it isn't of much practical significance. I know these things to be true because I've spent two decades with him. I'm
so lucky that my score didn't intimidate him or make him feel insecure!!

And, no, while both eligible, neither of us has ever belonged to MENSA. We met in graduate school. Which is sort of like MENSA for more pragmatically-motivated gifted people, frankly.
We are adults. Learning as adults is frequently about
desire for self-improvement/enrichment far more than it is about ability or grouping with age-mates. My husband and I are both curious and like learning and pursuing our passions (which are varied and esoteric). That trait is something we have in common. The same might be said of a friend with an IQ of 115, though, if that person is also curious and shares some of my interests, and might be untrue of someone with an IQ of 150 who happens to (in my estimation) be an arrogant, closed-minded jerk.
IQ is quite a crude tool for understanding likely differences in necessary
educational environments in children. I'm not convinced that the information has much meaning for adults. It
does have the potential to create barriers for us psychologically, however, and that is why I'd urge some introspection about the 'why' of such a desire.
Why not proceed on the basis that your suspicions about yourself are true and pursue life on those terms? Why not begin living as though that number were what you think that it SHOULD be? What could be wrong about that?
I hope that you don't find this offensive; it isn't that I'm saying that you are not
correct in your personal insight into your previous underachievement. I'm just saying that there may be a dark side to actually knowing, and I'm not really seeing what the benefits would be.
If you have never had a chance to do so, you might consider reading about
Dabrowski's Theory of Positive Disintegration. I suspect that you may be a relatively young adult (?), and if so, it is entirely possible that what you're experiencing is perfectly normal in that context.