yes, you won’t be able to deduct more than 15,500 off your tax return. The $15,5000 limit is a personal limit. If you were to try 1) your return would be rejected and 2) you would be penalized for not having the money refunded by April 15.

Tell your new employer what amount to limit you to based upon your YTD deferrals on your final check ast your previous employer.

Yes, and you will have to keep an eye on it as your new employer will not know what you have done during the year at your previous job.