If I have a 1 1/2 or 2 star player with poor stats it seems it is better to just fire him vs pay 2500 plus tax to sell him. Am i wright in this assumption?

Generally, PHI is right, player with talent below 3* won't be future players of higher level teams. You should focus on players with future BPOS of 4.5* --> talent 3.5*+.

But in your case, you should keep the players you have until the point a) you have enough money for buying either talented and/or skilled players b) your squad is that developed that you can fire him.

For me personally, i kept one player with 2* talent until one month ago 'cause he still has been better overall than my upcoming future players.
So, when you get to the point, that you have better players, fire him (or sell him, if his stats are reasons for other teams to buy him).