The only plane India could ever purchase from America is the F-35. The SH-18 and F-15 is a joke offer compared to the Rafale given the 2 billionish they spent on India modifications and already having 32.
The foremost being the SH and F-15 will not receive the kind of funding after 2045 that the IAF will expect for MLU. And there's a good chance the IAF will be expected to pay for the continued development of the jet. Even in the USAF, the F-15 received some upgrade funding only because the F-22 program stalled, and a lot of the more recent funding for the development of the F-15X came from outside the US, mainly Saudi Arabia, also orders from Japan. The SH will also not get the required funding post 2050. This is one of the main reasons why both SH and F-16 were rejected. All the teens are now senior citizens.
Otoh, the French have planned a Rafale F5 and even an F6, meaning they have a pretty long procurement plan that will outlast the IAF's procurement plan. So further development is practically assured, the same as the F-35.
Anyway, what our previous air chief said a few days ago--
Pakistan’s version on F-16 a facade, says former IAF chief BS Dhanoa
We evaluated the two US-made fighters and rejected them. Only Rafale and Eurofighter met the operational requirements. The American aircraft are good, but those are the F-35 and F-22.