Shift from big to small is instantaneous but it should take two clicks to get there, the second being as it hits the stop. When it is in the big ring you should be able to cleanly access (no front derailleur rub) the entire cassette, smallest to largest cogs, without touching the front derailleur.
The move from small to big is equally instantaneous providing it is adjusted correctly. Depending on where the front derailleur is positioned (1st, 2nd, or 3rd position), it can take from 1 to 3 clicks to get to the big ring. First position (most inboard) takes exactly 3 clicks to move cleanly to the big ring. 2nd position takes 2 clicks, and if the front derailleur is in the 3rd position (while on the small chainring), it should take just one click to move to the big ring. Sounds like an adjustment issue. The 2015+ front derailleurs are quite different in their setup than the pre 2015 front derailleurs. Sounds like you need a redo of your adjustment. But first, as a quick troubleshoot to rule out a couple things... back off the outer limit screw of the front derailleur, a lot, just to make sure it is not causing the difficulty in moving from small to big chainrings. I'm also going to assume the front derailleur is attached to the frame correctly and it's outer plate is dead, exactly, perfectly, right on, (do you get the importance of this yet) parallel to the large chainring. If it still doesn't move from small to big ring as it should, you need more tension on the cable. Do you have the inline adjuster installed? If so, with the chain on the big ring up front, and on the largest rear sprocket, adjust the tension till the inside plate of the front derailleur cage is almost, but not quite, touching the chain. Rotate the crank a few revolutions to make sure there is no rub. That's a quick and dirty synopsis. Is your mechanic well versed in post 2015 Campagnolo, or is he just "guessing" or doing it like he always has for the pre 2015 stuff? If it's one of those scenarios then he needs to educate himself on working with the newer stuff or you should take it to someone else more familiar with doing it correctly. Campagnolo has all their technical documentation online.