Did not swim (save for swimming lessons) until I went to highschool. We swam 6 months per year, 8x per week, but maybe only 8-10 hours total. The other 6 months we didn't swim. I payed no attention to sets, or technique, or what we were doing. Just swam hard, tried to catch people ahead, etc. Did that for 4 years and improved a lot. I think my first 100yard race was 1:18 (all out, dive, speedsuit, etc). By the end of 4 years I was 50.16. From then I swam much less, and now I swim 3-4x per week, for 12 - 15km.

The lesson I'm trying to get across is this: It will probably take a lot of investment, and probably a few years (maybe 2 swimming constantly), but the gains will stay with you forever (for the most part). I could likely swim a 25min 2000m on two swims a week now. Join a group... heck join two as I find most masters groups only meet a few times per week. Go and hammer it in the pool and, while you should focus on technique to an extent, don't be overly critical all the time.

Edit - I should add, I swim less now racing as MPRO than I did racing as an AG athlete. More time on the bike and run. Make the investment and you won't have to do much to maintain it.