Rating is tougher to gain the higher you get and yes there is a noticeable difference from 1800 to 1500. I'd say the biggest difference there is that a 1500 typically has little to no positional knowledge; their information is mostly to avoid isolated pawns and try to get your pieces developed actively. This is good advice, but an 1800 player tends to understand this further.
A typical 1800 will have a much deeper understanding of pawn structures (specific formations and opening structures rather than just realizing doubled or isolated pawns etc.) and we able to exploit square weaknesses more consistently - whether that be attacking a backwards pawn or simply making use of a weak color complex around the enemy King after their fianchetto Bishop has been exchanged off for yours.
Of course a 1500 is still really good compared to the "average" chess player rating and of course even an 1800 isn't always correct in their plans or assessment of the position, but their is a noticeable gap in positional understanding I'd say. Personally, I wasn't even thinking in terms of square weaknesses and outposts until I was roughly 1600 on chess.com rapid and even then it wasn't until about 1800+ where I could do something about my observations fairly consistently.
Chess learning is a process. Enjoy the chess journey and keep the emphasis on improvement and learning rather than on specific ratings 
The past 2 years I've averaged gaining 300-400 points per year on my Rapid rating. I just hit 1500 and I'm curious how long it took everyone to hit 1800? I've been really focusing on improving my game the last few months and I've seen a lot of improvement. And those of you around 1800, do you see a big difference between 1500 and 1800?