15 Day Itinerary Help - need suggestions!!

Too much too fast. You are changing locations every couple of nights and will spend a great deal of time checking in/checking out and moving to a new city. If Vicenza ia a must, drop the south and do a good job on the north (Rome and points north). Day 1 - fly into Venice; spend 3 nights Day 4 - to Vicenza; spend 2 nights Day 6 - to Florence; Spend 4 nights and get to Siena, maybe a hill town Day 10 - to Rome; Spend 5 nights
Day 15 - fly out of Rome If 5 nights in Rome seems like a lot, take one day and do a long daytrip to Pompeii. You cannot see everything in the time you have, so don't try. You'll enjoy the trip more if you are not constantly re-orienting to a new location.

Count nights on the ground, not days, and try to stay at least 2 nights at each location. Changing hotels too often is a time waster (packing/unpacking, checkin, checkout). I would do (assuming same places you mentioned): NIGHT NUMBER: Sleeping locality: Arrive VCE 1: Venice 2: Venice 3: Vicenza 4: Vicenza 5: Florence 6: Florence 7: Florence (go straight down to Naples area from Florence bypassing Rome) 8: Naples area (Sorrento, Capri, Amalfi coast, Pompeii) 9: Naples area 10: Naples Area (go back up to Rome) 11: Rome 12: Rome 13: Rome 14: Rome
depart to US. You can add or subtract nights to the locations as you wish, but try to leave at least 2 at any one location (2 nights = 1 full day, dawn to night, in that place). Rome needs at a minimum 3 nights. The departure to the US is early morning, so the last day cannot be counted and the last night you need to go to sleep early.

Thank you so much! This really helps!

If you really like your brother in law, you could spend all nights at the beginning in Vicenza and none in Venice. You can visit Venice from Vicenza. Venice is close enough to Vicenza for easy day trips by train. If you don't like your brother in law that much, you could stay the entire first 4-5 nights in Venice and visit him in Vicenza from Venice. I would opt for the second option, also because Vicentini are known for eating cats. Proverb from Veneto: "Veneziani gran signori, padovani gran dotori, visentini magna gati, veronesi tuti mati, trevisani pan e tripe? rovigoti baco e pipe...
E Belun? Poro Belun, te xi proprio de nessun! (Venetians great lords, Paduans great doctors, Vicentini cat eaters, Veronesi all crazies, Trevisani bread and belly, Rovigotti tobacco and pipes...And Belluno? Poor Belluno you are nobody's!)

Dont waste time traveling and back tracking....save Rome to the very end, instead of breaking it up on days 8&9 and 14&15. I think you can also get to Pompei from Capri without too much time/travel, so do it on one of your days in Capri and add the day you have for Pompei to Venice for a total of 3 nights.

Ginnie, my best advice to you would be to follow Roberto's advice - he knows whereof he speaks. Especially about spending 3-4 nights in either Venice or Vicenza and doing day trip/s to the other, so much more relaxing than moving every couple of nights.

Ditto that about Roberto's advice. I get such a chuckle our of his informative and many times humorous posts!