They certainly have, but the general idea is to first use stealth jets to bomb defensive systems (including radar observability) to conquer the skies, and then you can fly around somewhat freely. While SAM technology has improved, so have America's observability and stealth bombing capabilities. It will be interesting to learn the context and sequence of events which led to an F-15 being shot down by enemy fire.

(In 1991, the United States relied on the F-117 Nighthawk to penetrate Baghdad and launch salvos against radar and SAM sites. Simultaneously, Tomahawk cruise missiles were fired against similar communication and defense sites. In this war with Iran, the F-35 and B-2 have been used for stealth missions).