I can't see why you would want to climb to circuit height before turning downwind. The only rationale I can think of is so that you will not be climbing into traffic that is already established on downwind. However if the effect is that you are flying a wider downwind than the traffic in question, you can still be climbing into it anyway (as your crosswind intersects their downwind). It's not something I've ever heard of before. If you're flying something low powered (152, Citabria, etc) then you'll end up flying downwind in the next county!
Similarly it makes perfect sense to start decsending abeam the threshold, if there is no other traffic to fit in with. That's the way it's normally taught in the US at least.
The other day I was flying patterns in a Citabria, mainly to remind myself I can still fly a "normal" taildragger since the weather was too poor for acro. A lot of fun, but I ended up flying 500' patterns because otherwise it took forever to get to 1000', then it was time to start down because otherwise you end up flying a maximum slip all the way down final!
15 degree AOB sounds awfully shallow. I can see why people might teach it that way, so they NEVER get to watch their students stall and spin into the ground, but it's EXTREMELY conservative and imo it isn't good practice. I was taught to fly 30 deg banks in the pattern. I'd strongly recommend getting some stall/spin training so you feel confident about recovering if you ever DO get close to a stall. At 30 deg, stall speed is less than 5 knots higher than level so you still have a huge margin. I don't know the exact stall speed for a PA38 - I've only ever flown one once and I certainly don't plan to repeat the experience - but assuming it's below 50 knots, at 70 knots you won't stall until you reach 60 degrees of bank. Get an instructor and go try it, at altitude of course. Accelerated stalls are a bit of an eye-opener but once you've done a few you'll feel a lot more confident.
n5296s