I think you can definitely do it! I am also 30 and pretty big for a runner 6'1 173 and happen to be chasing a sub 15 for the first time since I was 19. With regards to volume I think that you have enough aerobic background to drop down to 65-70 a week in order to get in harder workout days. That being said the reaction to reducing mileage is very individual, for example, I tend to run a lot worse when I drop below about 70 per week. If you are like me your might be better off just slowing down on your easy runs and keeping mileage constant.
I think that the earlier advice about getting comfortable at race pace was pretty smart. Anecdotally, when I broke 15 for the first time I was a senior in High School and I was running shorter races quite frequently. In the two months leading up to my sub 15 I ran the following series of races:
1500 - 4:04
8K XC- 26:01
1600 - 4:22 (relay split)
3200 - 9:18
dual meet triple 1600 - 4:30, 800-2:05, 3200 - 9:59
1 mile - 4:21
dual meet double - 1600- 4:21, 3200 - 9:26
dual meet (3 days prior to sub 15) 3200- 9:34
Basically, that series of races served as my race pace or faster work. So when I got on the line to run the 5000 I knew, with absolute certainty that I was at least going to make it to 3200 on pace. I had just run 9:34 that Wednesday (before a Saturday race) feeling totally in control so mentally it was a breeze to come through 3200 on pace in 9:36.
I would never try to recreate what I did to break 15 in HS now as that amount of intensity would not allow 30 year old me to recover. However, I am definitely going to try to run 3000 or 3200 at 15 flat pace feeling completely relaxed 8-10 days before I take a shot at sub 15 this fall.