Here are my corrections, Swetlana:
Thank you for the kind words. I've done my best to share my knowledge with the new team, and I feel confident that they are prepared to continue working without my support.
I also wanted to say that it has been an invaluable experience to work in a large American company, participating in company processes, and to be a member of the fantastic "Company-X" team. I am grateful for your professionalism, guidance, and encouragement. Thank you.
Notice:
- I used a contraction (I've). This helps create a semi-formal style, which is appropriate for an "exit" speech like this.
- I changed "big" to large ("big" can sound a bit informal)
- "Thank you for the kind words" is almost a set phrase, a lexical chunk, in English
- I used "company" like an adjective in "company processes." This sounds more professional, in my opinion.
Your speech was well-written to begin with, but I think my suggestions are helpful. Good luck with the speech!