D154 in and of itself could mean more than 1 thing. For example:
Wilwood bolt-on front brake conversion kits are designed to provide superior braking performance and a highly detailed appearance over a wide range of domestic and import applications. D154 Front Caliper Kit
www.wilwood.com
If the stock caliper piston was 2.5" then a stock piston has an area of 4.9 sq/in. OP replaced that with calipers with an area of 4.12 sq/in and thus downgraded.