Transactions take way too long, and are too expensive for a globally adopted currency.
I suggest you start using bitcoin before giving an opinion about its speed and cost.
Bitcoin as a payment system, currently has the fastest transactions among all payment systems including the banking system. The transactions reach their destination immediately (1-2 seconds) and on average it takes 10 minutes for them to become finalized.
In comparison in the traditional systems like the banking system, it takes months for the transaction to be settled and become finalized and same with altcoins considering they need a lot more "confirmation" compared to bitcoin to be considered final and that usually takes hours.
As for transaction fees, in 99% of bitcoin's lifetime the fee has been very low. Currently a normal bitcoin transaction costs about $0.03 which is very cheap.
Come on, 1-2 seconds? In a utopia maybe. In reality purchasing anything you will need to wait for network confirmations, which can take multiple hours. I've used Bitcoin countless times. Comparing that to the traditional system, my transactions don't take hours, rather seconds.
The average transaction fee per 1 September was $1.09, where do you get a $0.03 instant transaction on Bitcoin mainnet?