It's usually best not to try to persuade a partner. Initial resistance is high, and it will end up projected on you. That is, your partner may perceive that you are trying to take away his/her pleasure in life.
A better approach is to explain that, although your sex life is fine by regular standards, you want to experiment with avoiding orgasm *yourself* for a few weeks, to see if you notice a change in your mood when you resume orgasm thereafter. (NOTE: Trying to avoid orgasm without explaining what you’re up to, is likely to lead to misunderstandings, miscommunication and resentment.) What is it like for you? What do you notice?
Meanwhile, ask your partner's opinion about the concept of karezza, by offering some reading material. Possibilities are Cupid's Poisoned Arrow: From Habit to Harmony with Sexual Relationships, The Karezza Method, and any of the Science articles in the left-hand margin (click on "Science" at the top of the page first).
Experience has shown that both partners have to understand, and be willing to try, karezza to see benefits. If you plant the seed and don't push, it may sprout later.