This is a question asked by every person who got attracted by Telegram features. As i have been using this TG for 5 years i can give you a few tips.
Easiest way is to tell them to install and try it once . They would say several excuses like Low memory , Theyre already using too many messaging apps etc.
Send them an article explaining Telgram features like the one i write in Medium.
b. Large file sharing
c. Instant View
d. Large groups
e. Animation Stickers
If Still he is not interested , you can leave the topic because you dont need to force anyone to use anything people will use what they feel useful. At last we all are users of an app. Its not our duty to work as Telegram marketing team.imo TG only focus on organic growth.