TOEFL speaking section tips for non-native speakers — what actually works?

The speaking section of the TOEFL iBT is genuinely the hardest part for me. I can write essays with no major grammar issues, but when I hear the timer start I freeze and my sentences come out jumbled. The 15-second preparation time for integrated tasks feels impossibly short.

I have been doing two things: recording myself answering practice prompts and listening back critically, and using a template structure for each task type. For task 1 (independent), I use an intro sentence, two reasons with brief examples, and a quick conclusion. This keeps me on track even when nervous.

The mock tasks available on the TOEFL Speaking and Pronunciation practice set helped me get used to the format. My main question: is it better to use more complex vocabulary and risk stumbling, or use simpler words delivered fluently? Raters seem to value delivery over vocabulary range.