If you apply for H/KOOC-0/B on April/KOOC-0/5, and if approved, your H/KOOC-0/B will take effect on April 20/KOOC-0/5/KOOC-0/0/0, then you can keep working and balance the transition.
If your 20 15 H 1B is not approved, but you have to wait until 20 16, you can only work until the end of your OPT. After OPT ends, April 20th 16 will be 1 (if you wait until April 20th 16, 1), your identity will be illegal, but from April 1 until H 1B, whether you have an identity or not. If you have no identity, H 1B is rejected, and you only have a few days to change your identity or leave the United States. If you have no identity and H 1B is approved, then there is no problem.
If you change your identity, you can reapply for the school and stay in the school, but you can't work.
The approval of H 1B depends on whether you need to go back to China to apply for a visa and then come back. Some exchange students who have changed their identities (mainly referring to those who have been approved to apply for H 1B after changing to F 1) need to go back to China to apply for visas.