4 years. I got into Resident Evil franchise with RE4 in 2015 after getting disappointed with DMC4 Special Edition. ( The game was still a half game and I remember being extremely disappointed with this decision due to DMC4 being my 1st DMC game and having a special place in my heart. )
After finishing RE4 and liking the hell out of it, I eventually bought RE5 and finished that too. I remember getting disappointed and having frustrating situations with it which was mainly due to partner AI and the game didn't feel as satisfying to play as RE4.
Some time passed; and I wanted to buy RE6 and check the reviews for it. However the reviews were really mixed; it was a situation similar to DMC2 / DmC, the games that I found terrible and hated with a passion. Since RE5 was disappointing after playing RE4, the reviews kept me away from the game along with the franchise for a couple years until RE7 was released.
With the release of RE7, I bought the game and finished it. I remember enjoying the game more than RE5; ( but not as much as RE4 ) but I remember getting confused about the story. It had such a weird tone to it and I couldn't explain it to myself until I replayed RE games. ( Of course my enjoyment drastically decreased unlike RE5 which grew more on me after replaying RE games a couple of times. )
Before the release of RE2 Remake; I finished playing all mainline RE games and my reason for getting interested into playing more RE games was TGBS' " Why RE6 is awesome? " video. I wanted to try RE6 but before that; I wanted to know what happened in RE timeline pre-2004 so I played Remake, RE2 and RE3. ( I played the last 2 on an emulator. ) I liked the hell out of those games and after playing those; I bought and played RE6. To my big surprise; I also liked that game and it felt like an improvement over RE5 in many ways, including in Chris' campaign which I felt wasn't as fun to play as other campaigns.
After that, I learned there were more mainline RE entries other than numbered entries and also finished them before the release of RE2 Remake. Only really liked RECV; RE0 and Revelations were extremely boring. RE1 was good but didn't age that well and Revelations 2 had some fun parts, mostly in Barry's campaign.
Eventually I played RE2 Remake after the game got released and it was kind of a disappointment.