It's true that most of your tutorials will be in college (except options in third year, which are a different kettle of fish), but in terms of contact hours (i.e. not self-study time), you are likely to actually spend more time in lectures than in tutorials. This is because the typical Law undergraduate has 3 tutorials every 2 weeks, or 1.5 hours/week of contact time. In contrast, lectures, which are almost always at the Law Faculty, run Monday-Friday (see
https://www.law.ox.ac.uk/sites/files/oxlaw/michaelmas_term_2017_final_draft_for_website_4.pdf for a sample, particularly the Law Moderations section).
That being said:
(a) all lectures are completely optional. You can choose to attend as many or as few as you like.
(b) you will spend far more time doing self-study than in lectures/ tutorials, and you can easily do this in college if you prefer. College libraries should have most of the law books you need, although on occasion you might have to go to the Law Bod, which is in the same building as the Law Faculty.
I do agree that your sense of commute time gets warped somewhat at Oxford because most places are so close to the city centre - I would be thrilled to live an 18 minute walk away from work now!
Worcester is absolutely an awesome choice though (and so is John's). I know people agonize a lot over college choice, but in truth pretty much everyone ends up loving their college anyway, regardless of whether they picked it or not.
Good luck!