Welcome from me as well. Tom has given you guidance as good as you will find anywhere. If you went to a coach at your local pool, I don't think you would receive suggestions as helpful as those Tom has given.
I will add a couple of suggestions
1) Focus on your 1500m time, rather than 1600m. Why? Because this is what's called the 'metric' mile and is an officially recognized racing distance, which will give you far more opportunities to compare your results--and progress--with others. The 100m difference is negligible so your 'true mile' pace will likely be the same in the end. In 25y pools, the metric mile is 1650y. Either 1500m or 1650y are conducted at all important meets, including Masters.
2) Swim the full distance far less frequently, perhaps once a month at most. You will progress far more steadily if the bulk of your training is broken into distances no greater than 1/3 to 1/4--but generally much less--of your goal distance.
You can break up 1500m into 3 x 500, or 3 x 400 + 1 x 300.
Even better would be
5 x 300
2 rounds of (5 x 150)
Best of all would be
3 rounds of 5 x 100, with an easy (Perfect!
) 50 between rounds. Click here
for an example of me doing this exact set yesterday.
And finally, Tom's first suggestion was the one that will make the biggest and most immediate difference. Reduce energy waste so your current 100m pace becomes so easy, you can then hold it for 200, 300, 500 and eventually 1500m.
For that I suggest our Self Coaching Toolkit