Yep, i.MX6SLL devices are running on 4.1.15
A Forma on FW 4.14:
Code:
Linux (none) 4.1.15-00280-g3c80cbc #75 SMP PREEMPT Thu Feb 14 09:20:03 CST 2019 armv7l GNU/Linux
This is also the same kernel release used by Amazon on their own i.MX6SLL/i.MX7D devices (PW4, KT3; KOA2). Which probably tells me they're both based on NXP's.
Bonus points if you can suss out where NXP's hiding those sources. A (very) quick search led me to old FreeScale branches, but nothing new...