Sarries led the way throughout the season, with a run of 12 straight wins at the start leaving the other 14 clubs trailing in their wake.
But defeats to Wasps and Harlequins - who they meet in Saturday's final at the Trailfinders Sports Ground, in Ealing - meant a nervy end to the season.
Marlie, who has more than 50 caps for England, was speaking to former Wales and British and Irish Lions star Richard Hibbard, after HomeServe installed a range of smart home technology at his home in South Wales.
She said: "The first season of the Premier15s has been good and has lifted everyone's game. We had some extra clubs coming into the league which has been great. They've all been top six and Gloucester-Hartpury have been top four.
"Part of this year's programme has been getting all the clubs to operate with a professional club set-up. That means strength and conditioning, physios, and that sort of thing.
"With another year behind us, that will be even better.
"The main lesson we have learned as a team is not to become complacent. We were smashing it at the start of the season but in the last few games we took our foot off the gas.
"When we lose four or five players to international duty - like Poppy Cleall and I - other players do step up and give us some go forward but I think we just lost a bit of that."
Marlie also discussed the recent Six Nations, in which England finished second to France after losing in Grenoble to a last minute try.
She added: "We were really disappointed with the result. France was a really tough one because we felt we lost the game rather than they won it.
"It wasn't that they played much better than us. We wasted five killer opportunities to get points but it's one of those things.
"We were pleased to finish on a high with a game against Ireland in front of one of our biggest crowds."
Video: Marlie and Richard Hibbard chat about the inaugural Premier15s season and the Six Nations - view this video here INSERT LINK
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