People misuse Mark 1:15 by attempting to add "of your  sins" into the verse itself.

Mark 1:15   KJB
[15] and saying, The time is fulfilled, and the kingdom of God is at hand: repent ye, and believe the gospel.✅

Vs

Mark 1:15 according to the turns from sins crowd/repent-of-sins-to-be-saved crowd that we deal with: 
[15] and saying, The time is fulfilled, and the kingdom of God is at hand: repent of your sins, and believe the gospel.❌

Mark 1:15 literally says repent....and believe the gospel. Meaning, you didn't believe the gospel before and now you do believe the Gospel.

Adding "of sins" into the "repent ye and believe the Gospel" in Mark 1:15 twists & perverts biblical repentance (a change of mind) into the works salvationism heresy of repent of/turn from your sins!

@RepentOfSinsExamined