There probably won’t be the market crash that most people are predicting (or hoping for) but you should see a dip in player prices as people clear out their squads looking to free up fifa 15 coins to buy TOTY packs.
The exception would be the very top players. Messi and Ronaldo have already dropped 200K in value at time of writing (although their prices were already really inflated) and could drop even more leading up to the release of the TOTY strikers. It should definitely be a buyers market.
The FUT market price dips aren’t just directly down to TOTY though. Indirectly, in the ‘black’ FUT market coin sellers are hiking up their prices in a bid to cash in on people’s rush to stock up their coins for TOTY packs which will have a noticeable knock on effect to Ultimate Team trading.