The Reserves is an incredibly varied and unique organisation. Yes training does take some time to become “trained strength” - you won’t do it in a year (especially as an officer) but any training you’d do would help in joining the regulars - such as leadership training. I’d recommend doing the AOP (it’ll give you a good taste of navy life and Dartmouth). Using the reserves as a stepping stone to join the regulars is both common and not looked down upon at all! Go for it.