I'm in the process of writing an extensive review of the T15. I was hoping to have it done by now but work has been keeping my busy. Should have it done in a week or two. I'll be writing about the T15's performance on a three month residential remodeling job. Here's a spoiler, the T15 is nearly a perfect tool, I say nearly because it's human nature to always want more. There isn't a better cordless drill out, sure some drills are more powerful but they lack the refinement of the T+3 series.
Drilling steel, no problem with the 5/16" mild steel I drilled. Tough, you bet, I tested that out the first few days of owning the T15. Dropped it twice, once from 9' and one time from 6' onto a wood floor. The drill didn't skip a beat. I can vouch for the dust test Martin talked about, not with Arizona sand but with plaster and coal dust from demoing walls in a 125 year old Victorian. Dust was everywhere, my drill was covered for days. No, don't baby a Festool drill, no need. Keep an eye out for the review in the couple of weeks.