Fantasy football playoffs start in Week 15 for many leagues, while others begin with the semi-finals in Week 16. Either way, now is not the time to take a break on making your roster the best it can be. NFL teams are putting forth their best players during crunch time and you should be doing the same in fantasy.Fantasy Football Week 15: Start 'Em Sit 'EmIt is not as simple as just putting the top-ranked players in each week, as they can face unfavorable matchups and end up as a dud. Here are a couple of the best and worst matchups to watch in Week 15 for your fantasy football lineup.Start 'Em - Best MatchupsQB Tua Tagovailoa - vs New York JetsPFF MIA Dolphins@PFF_DolphinsTua Tagovailoa: Highest completion % among all QB’s when kept clean this season (77.3%) 🔥2:23 AM · Dec 13, 202174983Tua Tagovailoa: Highest completion % among all QB’s when kept clean this season (77.3%) 🔥 https://t.co/Dav9qAJssrThe Miami Dolphins are coming off a bye week to face another bye week, in a sense. They face the New York Jets, who have given up 63 total points in their last two weeks and haven't had a takeaway since Week 12. Quarterback Tua Tagovailoa was very efficient with the ball against the New York Giants in Week 13, going 30/41 for 244 yards and two scores. Tua hasn't thrown a pick through his last two games but also hasn't thrown for more than 275 yards in a game since Week 7. The Dolphins' top three running backs are on the COVID-19 list and could likely throw the ball 40+ times against the Jets' weak secondary. It might not be pretty, but it seems like easy points to grab for fantasy players.WR KJ Osborn - vs Chicago BearsMinnesota Vikings@Vikings💣💣💣@KirkCousins8 airs it out to @KJ_Osborn#ProBowlVote 📺: @NFLonFOX11:13 AM · Dec 9, 20211362238💣💣💣@KirkCousins8 airs it out to @KJ_Osborn#ProBowlVote 📺: @NFLonFOX https://t.co/B9llB8aJ3PKJ Osborn has risen to the occasion for the Minnesota Vikings recently, racking up more than 14 fantasy football points in each of his last two games. He had 83 yards for a touchdown against the Pittsburgh Steelers last week and now has another great matchup against the Chicago Bears this week. Adam Thielen is not expected to be ready to play this week and Osborn will be a featured player again. He's being labeled as a WR3 in fantasy football with a ceiling of 14+ points again. Just hope quarterback Kirk Cousins doesn't have another meltdown this season.Sit 'Em - Worst MatchupsRB Dontrell Hilliard - vs Pittsburgh SteelersAdam Koffler@AdamKofflerDontrell Hilliard just dropped a screen pass that absolutely had a chance to go to the house3:40 AM · Dec 12, 202191Dontrell Hilliard just dropped a screen pass that absolutely had a chance to go to the houseThe Pittsburgh Steelers have been one of the worst teams in the league against the run lately, but Dontrell Hilliard still faces a poor matchup. The Tennessee Titans are using a rotation of three different backs and Hilliard currently ranks third in the group. Jeremy McNichols and D'Onta Foreman had more touches than Hilliard, allowing him to have just over one fantasy football point against the Jacksonville Jaguars last week. The Titans could run the ball more against Pittsburgh, but it is anyone's guess on who ends up being the leading runner this week.WR Marquez Valdes-Scantling - vs Baltimore RavensJake Trowbridge@JakeTrowbridgeAaron Rodgers tries that same damn throw to Marquez Valdes-Scantling multiple times every game and it works exactly 3% of the time.9:39 AM · Dec 12, 2021342Aaron Rodgers tries that same damn throw to Marquez Valdes-Scantling multiple times every game and it works exactly 3% of the time. https://t.co/h1eYnG4icdEveryone expected MVS to have a big game against Chicago with Randall Cobb out, but he caught three of his five targets for just 20 yards, totaling five points in fantasy football. For those who placed in at FLEX, we feel your pain. The Green Bay Packers face a weak secondary in the Baltimore Ravens this week, but MVS is not a streaming option. He's seen as a touchdown-or-bust player in fantasy football this week.Also check out: Complete Monday Night Football Schedule 2021