I'm with Jim. If you want a tub/shower unit, then you need 5' wide plus a half foot for the wall so figure 5.5' wide for the bathroom. Length will need a half foot for a wall plus 2.5 foot for the toilet plus 32" for the tub plus your vanity. Basically 5.5 feet plus the vanity which a 30" vanity is a nice size so you get about 8'. Could get it down to 7' with a smaller vanity. You can save room with a shower only but not much. The stool sticks out about 2.5' and then you need room to walk in and sit down without bumping your head and knees on the wall (same for standing in front of the vanity) so you are still at a bathroom of 5' wide for the toilet unless it was stuck in there at the end for which there wouldn't be room for a tub or shower. this is figuring on using a 24" door.
Like Jim said, the balance would make good closet space with bifold doors. Think about part of it as builtins with shelves and drawers for linen and clothes storage. Look at different closet storage options at the home cheapos.
I've seen many bedrooms 9'by 10' (usually the 2nd and 3rd for kids) so a 9.5' by 15 foot bedroom gives you plenty of leg room at the end of the bed and room for dressers.
The limiting factor on bathroom location may be where all the plumbing is going to tie into and where the door presently is(of course you can move the door during the remodel). Good luck.