J-15s have to stay relevant in naval warfare.China placed nuclear powered carriers, air force and nevy fighters on top priorities first to counter dangerous US threat at the moment. STOVL fighter programme will start after stealth bomber (heavy fighter bomber) consecutively or concurrently.
It won't be hard for China because the same Yakovlev engineers that made F-35B STOVL could do the same for China. Single engine STOVL fighter most likely unless China wanted to try world's first twin engine STOVL large fighters. China would invest more into STOVL fighters because it could land on simple piece of flatlands should China decided to engage US in Pacific Ocean war. Heavy Tiltrotor is in China's mind too.
R&D involves trial and error involving billions to trillions. US made lots of fighters, choppers, ships in 50's, 60's, 70's, 80's that were short-lived spending much to contribute to technology perfection. You can see the same on J-10 development from A to B to C. J-10B built in small numbers and perfected further to J-10C that will go mass production. Even J-20B today is not finalized and subject to further modifications later in J-20C depending on how soon they could perfect the technology.
They have the capabilities to be a strike fighter for many years. However when matched with F/A-18 Super Hornets, it is debatable of who wins.
To catch up, China should implement more electronic warfare on the J-15s, like the Saab Gripen. They can give false radar data forcing enemy aircraft to engage in vision range combat. Destroying long range stealth advantage. Having some aircraft like the Growler on the 001/2 would help too. And I mentioned that upgrading radars to radars not yet invented for planes would be a great R&D task for the J-15s. They have ground radars that can track and destroy stealth at many Kms. These radars need to be miniaturized for PLAN/ PLAAF.
Keeping J-15s relevant keeps 001/2 relevant and extends their usefulness to the PLAN.
001s won't be useless for many years, look at how long we Italians have kept our small light carrier in service with only harriers and helicopters. We know the limitations and use only for strike and ASW.