It's not difficult, just time consuming and tedious. (Most of your time will be spent getting to the valves)
I usually dedicate a weekend to do mine, 3 days if I need to swap shims.
I pulled it apart at 15k and checked the gaps, they were all in tolerance but a few exhausts were getting tight, but I decided not to tear in further at that time, When I did the 30k I took it to a dealer that I could trust and had them re-set everything to the middle of spec, I'll hit 45 next year sometime (Haven't had time to ride sadly) I'll check them again.
Taking on to what some have already said (although without the colorful soliloquies
) I will advice you that your dealer mechanic is not offering good advice, but I would say you prob don't need to do it every 15k, every 30k is prob fine but you DO need to at a minimum pull it apart and measure the clearances, if they are fine then button it up and ride on, if not, well...better to do it now and have a long running engine