Samsung has seeded Android 6.0.1 update for the Galaxy Tab S2 8.0 in the UK with firmware version T710XXU2CPD9. This follows the bigger Galaxy Tab S2 9.7 getting its Marshmallow update
If you haven't received the update yet, just head over to settings and check for updates. Currently only the Galaxy Tab S2 SM-T710 WiFi variant is getting the update to Marshmallow with April's Security patch as well.