Yes, I have 14, 15, and 16 on Steam, running both on Windows on one computer and Linux on another. Using OOTP on Steam works really well for me, at least.
If the past is any indication, OOTP16 should be on sale for 50% off at the MLB all-star break, which is mid-July this year.
This is probably answered elsewhere, but is this league moving to OOTP16 at any point, or waiting for a future version?