question

1)if I switch, will the data of user will be lost and if it does, is there a way to carry the user's data from gamespark to playfab, so the user's data is not lost.

Yes, all data will be lost as GameSparks and PlayFab are two different platforms. You will need some additional work to transfer data form GameSparks to PlayFab.

For example, you can ship an update that let players log into GameSparks and PlayFab both. So you can establish a map between GameSparks account and PlayFab account. Then you can read data from GameSparks and store it in PlayFab. For PlayFab, you can refer to Player Information in Tutorials. And Brendan's answer here: https://community.playfab.com/answers/18831/view.html might also help you.

2) if I do, then how much time(month) it will increase to switch from gamespark to photon, playfab?

It's hard to say how much time this will take, that will depend on your game size, architecture and your development team. If you have any problem, please fell free to ask here.