You got that right, it’s uneconomical to trade small amounts as fees will proportionally increase; sum that with the spread of the offers, they won’t be really taken. You can check in Market > Trades to see the usual amounts, I’d say most common is 0.01btc, lower not so much.
The difference from the normal market price is due to the bisq market itself.
One day, if the volume of trades increases, there will be more competition between offer makers and the spread will decrease.
To your specific question, no, I don’t think yous 25€ offer will be taken easily, you might have to wait many days before it does.
This thread explains it well: How to make your offers more successful? - #7 by schizo