No you should not. Exchange rates for Turkish Lira will be much better In Istanbul than in your home country. If you arrive by air, you’ll see exchange offices as soon as you get through passport control. Also in the city there are plenty of official exchange offices. In addition credit cards are widely accepted in Istanbul. Other than for taxis and very small shops you can use your credit card for almost anything. ATM machines will be everywhere in the city as well and you can use them to get cash with your credit card in an emergency.
How stable is the Turkish Lira these days?