Oh, yeah, OCs are still common the UK. Those are totally snortable, so it's your call. 10mg is a pretty normal dose for an opioid naive person so you could have three doses there if you play your cards right, but should have at least two. Some people need more than 10mg, some need even less so better to start low and add later. You can always take more but never take less. Again the BA is higher by mouth but a lot of users swear they feel the same or better from taking the same amount by nose as they would by mouth... I always needed more when I snorted and studies do support that more is absorbed in the stomach/intestine *shrug*
If I were you I'd probably powder one of those pills and swallow about 2/3rds of it wrapped in a tiny piece of TP or otherwise just washed down with water. The remaining 3rd can either be added later if absolutely necessary or saved for use with part of the second pill. Taking the whole pill at once, even if you chew it up to defeat the time release mechanism, is unlikely to be *way* too much or anything... but 15mg can definitely be overwhelming to some naive users and personally I'd rather have an extra dose if I could get away with it.
If you're more of a snorter I'd still use about 2/3rds or even just half the pill since it's even easier to add more later when going that route IMO.
As for the fent, idk... but don't flush drugs into the water table. If you're going to get rid of it, get it all in one bag and duct tape all around it to cover it up and stick it in the bottom of the trash or something. Someone may have a better idea than this but whatever you do please don't flush a potent opioid.
I'd really think hard about fucking with any opioids if I were you but I'm not really in the business of stopping people from doing something they're determined to do. They really are life-ruiners, though. If you can use just these two pills and never look back that's great, but just keep in mind that every opioid addict started with a single dose and clearly you already like benzos. Just have a think on it at least.