@Angelo 

My experience to short in Italy i usually plan with atleast 20mins

How are you travelling? Wich trains? When? So we can give you some advice. How @seewulf says, in Italy better plan with 20 minutes. 

I'm using Eurail Global Pass. Travel on the 23rd June 10:11am, the train is IC505 (La Spezia -> Pisa Centrale) then 8 minutes transfer to RE4028 (Pisa -> Firenze SMN) before continuing to Venezia S. Luzia.

If 8 minute not feasible, then I plan to take the IC657 on 11:23, with a 15 minutes transfer at Pisa Centrale.

@seewulf thanks also for your italian daytrain seat reservation guide using OBB, will help me save  a few $2 reservation fee from eurail site

Toss a coin. IF train#1 is on time-certainly feasible (unless you are overburdened with 5 suitcases and using waking sticks) for normal settings-BUT in general treni in IT are not really known for being on time-more for being ´ritardo´. As such Pisa is not a very big stazione.

Thank you all for the advice 

Thanks for the nice words. @rvdborgt  was the one who told me it´s possible after that it was easy to do the guide Iam currently in my exams and not so much active :/

Thanks also @rvdborgt

The short answer is NO

Timekeeping on Italian Railways tends to be poor.  Long distance trains - especially the ‘Frecce’ - get priority, but get held up because they travel long distances and delays happen along the way.  The local ‘Regionale’ then often pull over to let them past .

I would always allow at least 20 minutes - preferably 30 - to connect, and longer still for a train with a non-refundable ticket or one that operates infrequently e.g. Milan/Turin to Paris.  Bear in mind too that many regional routes tend to have a 3 hour gap in services in the mornings between about 9am - 12 noon which can be a further complicating factor.