How to optimise code to read a large CSV file in C++?

Question

I am trying to read entries of my csv file into an entries vector whose data type is object OrderBookEntry, this is an object that stores the tokenized variables from the csv line which itself is converted through the function tokenise. My problem is that my csv file has around a million lines and it takes over 30 seconds to load, how can I reduce this?

This is my code that actually reads lines from the file and converts them into entries.

    std::vector<OrderBookEntry> CSVReader::readCSV(std::string csvFilename)
    {
        std::vector<OrderBookEntry> entries;
    
        std::ifstream csvFile{csvFilename};
        
        std::string line;
        if (csvFile.is_open())
        {
            while(std::getline(csvFile, line))
            {
                try {
                    OrderBookEntry obe = stringsToOBE(tokenise(line, ','));
                    entries.push_back(obe);
                    //std::cout << "pushing entry" << std::endl;
                }catch(const std::exception& e)
                {
                    //std::cout << "CSVReader::readCSV bad data"  << std::endl;
                }
            }// end of while
        }    
    
        std::cout << "CSVReader::readCSV read " << entries.size() << " entries"  << 
        std::endl;
        return entries; 
    } 

This is the part of my code that tokenises the read line

    std::vector<std::string> CSVReader::tokenise(std::string csvLine, char separator)
    {
       std::vector<std::string> tokens;
       signed int start, end;
       std::string token;
        start = csvLine.find_first_not_of(separator, 0);
        do{
            end = csvLine.find_first_of(separator, start);
            if (start == csvLine.length() || start == end) break;
            if (end >= 0) token = csvLine.substr(start, end - start);
            else token = csvLine.substr(start, csvLine.length() - start);
            tokens.push_back(token);
        start = end + 1;
        }while(end > 0);
    
       return tokens; 
    } 

This is the part of my code that converts the tokens into a suitable object to work with

    OrderBookEntry CSVReader::stringsToOBE(std::vector<std::string> tokens)
    {
        double price, amount;
    
        if (tokens.size() != 5) // bad
        {
            //std::cout << "Bad line " << std::endl;
            throw std::exception{};
        }
        // we have 5 tokens
        try {
             price = std::stod(tokens[3]);
             amount = std::stod(tokens[4]);
        }catch(const std::exception& e){
            std::cout << "Bad float! " << tokens[3]<< std::endl;
            std::cout << "Bad float! " << tokens[4]<< std::endl; 
            throw;        
        }
    
        OrderBookEntry obe{price, 
                            amount, 
                            tokens[0],
                            tokens[1], 
                            OrderBookEntry::stringToOrderBookType(tokens[2])};
    
        return obe; 
    }