The Secret Network v1.5 update did not introduce any breaking changes for developers, other than some bug fixes described below;
Fix secret message parsing when a message is plaintext in IBC (#1199)
Update Cosmos SDK 0.45.9 -> 0.45.10 & Tendermint 0.34.21 -> 0.34.22 (#1230)
Update IBC 3.3.0 -> 3.3.1 (#1237)
Fix nested attributes signatures (#1241)
Fix some protobuf type names (256d9b2)
For more details on this upgrade, check the official release.