Last HIM (Jan 2013) was 42 mins approx, with wetsuit. Cause was long and water rough but much slower than my pool swim at that point fore sure
Last IM (March 2013) was 1h15 min, with wetsuit. Swam just below 2 mins per 100m.
Regarding OWS I for sure have some “low hanging fruits”:
– swim straigther
– push harder, I tend to take it too easy in the swim leg I think
Regarding my typical week:
5 sessions of which one is a 1,5k recovery session just to get in the water. The remaining for is roughly like this:
– one session with longer reps at race pace
– remaining sessions mixing 50-100m reps hard as well as some 200s
For sure I do not suffer enough in swim training. In bike and run I do, in swim I just do not feel I can/want to suffer as much.
A.
I submit that your “1.5k recovery session” and the “session with longer reps at race pace” have very little benefit in making you a faster swimmer. Swimming slowly in training only ensures you’ll swim slowly in a race. Yes you do want to mix in some longer swims and not everything needs to be sets of 100’s on short rest, but frankly those kinds of sets are where you’ll get the most improvement. There’s a reason why there’s a pace clock on the wall at every pool 
In your OP you say you can do 100’s on 1:55 holding ~1:40. The goal then should be to periodically reduce that base interval like so:
Weeks 1-3: 10x100 @1:55. Each 100 is under 1:40 with the second 5 being faster than the first 5
Weeks 4-6: 10x100 @1:50. Each 100 is under 1:35…Weeks 7-9: 10x100 @1:45…
Of course it won’t always be 10x100, sometimes its 6x200 @3:50 holding 3:20’s, or 4x300 @5:45 holding 5:00. The point is though that on a regular basis (every 3-4 weeks or so) you try to extend yourself by putting your base interval faster.
The other key thing is maintaining consistent repeat times - or better yet, descending them. The first time you do 10x100 @1:50 you may start off going 1:35, by number 10 you might be 1:49. You want to strive towards number 1 being 1:35 and number 10 being 1:25. Then the next week drop the base interval to 1:45.
For sure this will be hard; your stroke will fall apart and sometimes you’ll just be touching the wall and pushing right off again. But becoming a better swimmer requires more than just logging yardage - it requires constant focus and effort. You not only have to set a goal for each workout but for each SET in each workout, and often each REPEAT in each set.
And just a note on technique. While it is very important, there is little benefit in having a pretty stroke if it means you’re swimming slowly. If you concentrate on interval based training and regularly dropping your base interval times you’ll be amazed at how you find the technique you need to hit those times.